Fix PropertiesComparer when properties are not comparable

[Dreamescaper]

Fixes #4933 .

Turns out the problem is not Dictionary specific. It reproduces even for something like this:

class TypeWithObjectProperty
{
     public object? Value { get; set; }
}

var actual = new TypeWithObjectProperty { Value = new ObjectA("WTF") };
var expected = new TypeWithObjectProperty { Value = new ObjectB(123.345) };

Assert.That(actual, Is.EqualTo(expected).UsingPropertiesComparer()); // PASS!!!

The problem is that PropertiesComparer didn't check for NotSupported result - it basically treated it like a successul comparision.

[Dreamescaper]

@manfred-brands
Could you please take a look?

[manfred-brands]

Should it not return the TypesNotSupported?
The idea is that if one comparer doesn't support items, it bubble up and the next comparer is called.

As the PropertiesComparer is the last, the result is likely the same.

[Dreamescaper]

Originally I returned it, but the error message is not very helpful. It prints root object type name, something like Can't find comparer for types 'TypeWithObjectProperty' and 'TypeWithObjectProperty'. In case of assertion failure it prints exact property, which is much more useful.

Plus if I return TypesNotSupported, it fails with NotSupportedException, AssertionException is probably more suitable here.

[manfred-brands]

It depends if we want to distinguish between comparing as different vs not being able to compare.

What does normal comparison do when comparing instances of different types?

[Dreamescaper]

In regular case, it's NotSupportedException.
Which makes sense - as I have explicitly passed two incomparrable values to an assert method, i.e. I have done something wrong.

In this case, however - I'm passing two TypeWithObjectProperty instances, that's a perfectly valid thing to do. I can't know if some deep down property values have different types - that's exactly what I'm testing. Therefore - it simply should be an assertion failure.

[manfred-brands]

One final thing. What does a regular compare on a dictionary with different element types return?

[Dreamescaper]

AssertionException:
Assert.That(actual, Is.EqualTo(expected))
Expected: <NUnit.Framework.Tests.TypeWithObjectProperty>
But was: <NUnit.Framework.Tests.TypeWithObjectProperty>

[manfred-brands]

Thanks

[Dreamescaper]

Oh, Dictionary, not object. Still,

Assert.That(actual, Is.EqualTo(expected))
  Expected and actual are both <System.Collections.Generic.Dictionary`2[System.String,System.Object]> with 1 elements

[manfred-brands]

Thanks. Nothing further.

[stevenaw]

Thanks for another contribution @Dreamescaper
Great test coverage.